Overview

Comprehensive Description

Nesting Biology

The nesting biology in Colombia and Ecuador was studied by Gonzalez et al. (2004).

Colonies are found above the ground, in disturbed areas. Most of the nests either lacked a defined entrance or had a single entrance; a single nest had five entrances, one of them more active than the others. Nests had from 1 to 8 active queens and up to 80 workers indicating monogynous and polygynous cycles as reported from the lowlands. Nests initially lacked an involucrum covering the brood but eventually developed an irregular involucrum of wax mixed with cardboard and carcasses of B. atratus and their associated beetles (Antherophagussp., Cryptophagidae). Bees also built pollen pockets attached to larval clusters for feeding larvae. The average developmental time from egg to adult (29.6 days) and the percentage of cells with two pollen pockets (63.6%) were significantly greater than those previously reported. The maximum pocket diameter was significantly smaller, about half of the size, than those diameters observed in lowland colonies. The ecological significance of

such reduction in size is still unclear but could explain the higher frequency of cells with two pockets in our colony. Nests maintained an internal nest temperature about 128C warmer than external environmental temperature. Several workers were observed constantly scraping and cutting litter on top of one of the nests. Previously this behavior had only been known in Bombus(Fervidobombus) transversalis (Oliver), a closely related Amazonian species. As in the lowlands, B. atratuscolonies at high altitudes seem to be active year-round. The beetle Antherophagussp. was found in two of the seven colonies observed. They are probably scavengers, but nothing is certainly known about their role within tropical Bombuscolonies.